Process and composition for making multi-layer golf balls using rigid uncrosslinked shells

ABSTRACT

A multi-layer golf ball and methods for preparing a portion thereof including a core having at least one core layer, a mantle having at least one layer including an amount of reinforcing polymer component and a resilient polymer component disposed concentrically adjacent the core, and at least one cover layer disposed concentrically adjacent the mantle, wherein the layer of the mantle is sufficiently rigid to inhibit the resilient polymer component from substantially altering shape prior to crosslinking. The invention also includes an elastomeric composition including a polybutadiene having a high molecular weight average and a predominantly 1,4-cis content, a free-radical initiator, and a reinforcing polymer component having a sufficiently low viscosity at a mixing temperature to permit substantially uniform dispersion of the polymer component with the polybutadiene and having a crystalline melting point sufficiently low to permit mixing while avoiding substantial crosslinking.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.09/678,018, filed Oct. 4, 2000, now U.S. Pat. No. 6,494,791, which is acontinuation of U.S. patent application Ser. No. 09/293,982, filed Apr.19, 1999, now U.S. Pat. No. 6,172,161, which is a divisional of U.S.application Ser. No. 09/048,348, filed Mar. 26, 1998, now U.S. Pat. No.6,093,357.

FIELD OF THE INVENTION

The present invention relates to a multi-layer golf ball and methods forforming a portion thereof including a core having a center with at leastone center layer, a mantle having at least one mantle layer including anamount of reinforcing polymer component and a resilient polymercomponent disposed concentrically adjacent the center, and at least onecover layer disposed concentrically adjacent the core, wherein themantle or at least one layer of the mantle is sufficiently rigid toinhibit the resilient polymer component from substantially alteringshape prior to crosslinking. The invention also relates to the polymericcomposition used in forming the mantle.

BACKGROUND OF THE INVENTION

Multi-layer golf balls contain a core, which may include one or morelayers of solid material or one or more layers of solid materialencompassing a liquid therein, and a cover. Optionally, an elasticwinding may also be used to form a layer surrounding the center toprovide certain playing characteristics. Such balls are known as “wound”balls. The multi-layer golf balls discussed herein include a core and acover. The terms “core” or “ball core,” as used herein, include a centerhaving one or more layers and a mantle formed of one or more layers. Theterms “center” or “ball center,” as used herein, include a solid and/orliquid mass around which at least a mantle and cover are placed. Themantle is disposed between the center and the cover, typically inconcentric fashion, with the cover being the outermost portion of theball.

A variety of golf ball compositions are known and used in variousmethods of manufacture. Unfortunately, these compositions and methodstend to produce balls that do not consistently achieve a symmetricalcore. See, for example, the discussion in co-pending application Ser.No. 08/943,932 by J. DALTON et al., which illustrates the poor centeringthat occurs in conventionally formed golf balls. This co-pendingapplication is expressly incorporated herein by reference thereto forthis purpose. Multi-layer ball production has been plagued by centerportions that become off-centered during the manufacture of such balls.Off-center golf balls are a hindrance to many players, particularlythose able to achieve great control using a symmetrical ball. This lackof symmetry is now believed to be caused, at least in part, by thematerials and methods conventionally used in forming multi-layer golfballs. A number of these conventional multi-layer ball compositions arediscussed below.

U.S. Pat. No. 4,781,383 discloses a solid three-piece golf ball made bycovering a core, which has inner and outer layers, with a shell. Theouter layer of cis-1,4-polybutadiene, zinc diacrylate, and zinc oxide isprepared by using a metal mold to prepare two hemispherical premoldedproducts, which are used to cover the previously molded inner layer ofthe core. The outer layer is then cured around the inner layer byheating the entire core before adding the shell.

U.S. Pat. No. 4,919,434 discloses a two-piece golf ball having a solidcore of more than 40% cis-1,4-polybutadiene and a cover having an innerlayer of 0.1 to 2 mm thickness and an outer layer of 0.1 to 1.5 mmthickness. The inner layer is a thermoplastic resin, such as an ionomer,polyester elastomer, polyamide elastomer, thermoplastic urethaneelastomer, propylene-butadiene copolymer, 1,2-polybutadiene,polybutene-1, and styrene-butadiene block copolymer, either individuallyor in combination.

U.S. Pat. No. 5,150,905 discloses a rubber composition usable in golfballs having at least one natural or synthetic rubber component,inorganic fibers subjected to surface treatment, and a non-sulfur typevulcanizing agent. The rubber may include known additives, such asorganic modifiers of various resins like cumarone-indene, phenol,polystyrene, acrylic, polyamide, epoxy, urethane, polyolefin, andsimilar resins. The rubber may also include long fiber reinforcingmaterial, such as fibers of glass, carbon, metal, quartz, ceramic,nylon, vinyl, polyester, aromatic polyamide, polyimide, and aromaticpolyether amide.

U.S. Pat. No. 5,253,871 discloses a three-part golf ball including anelastomer core, an intermediate layer of a thermoplastic materialcontaining at least 10%, preferably at least 35%, of ether blockcopolymer, and a thermoplastic envelope. The other copolymer of theintermediate layer is disclosed to be one or more ionomers.

U.S. Pat. No. 5,314,187 discloses a golf ball having a core, as well asa cover having an inner layer of a cut-resistant material such as anionomer resin and an outer layer of natural or synthetic balata and oneor more thermally crosslinkable elastomeric polymers.

U.S. Pat. No. 5,439,227 discloses a multi-piece solid golf ball having asolid core with an inner layer of a rubber and an outer layer of 100-50wt % of a polyether ester type thermoplastic elastomer having a T_(g) ofup to −25° C. and 0-50 wt % of an ethylene-(meth)acrylate copolymerionomer, and a cover of ethylene-(meth)acrylate copolymer ionomer.

U.S. Pat. Nos. 5,553,852 and 5,556,098 disclose a three-piece solid golfball with a conventional rubber center core, an intermediate layer ofthermoplastic elastomer or thermoplastic elastomer and ionomer resinmixture, and a cover typically of an ionomer resin, each portion havinga particular hardness and thickness.

U.S. Pat. No. 5,601,502 discloses a three-piece solid golf ballincluding a core of a center having an α,β-unsaturated carboxylic acidmetallic salt in an amount of 13 to 28 parts by weight based on 100parts by weight of base rubber and an outer shell having anα,β-unsaturated carboxylic acid metallic salt in an amount of 28 to 35parts by weight based on 100 parts by weight of base rubber. The baserubber preferably has a cis-1,4 structure of 40% or more, particularly85% or more.

U.S. Pat. No. 5,681,898 discloses a golf ball having a solid core and acover, with an intermediate layer including a first component of anuncrosslinked blend of n-butyl acrylate and ethylene methacrylic acidcopolymer, which is sold under the name NUCREL, and a second componentof a vulcanizate formed from polybutadiene and a peroxide curing agent.The vulcanizate is ground to a fine powder and then conventionally mixedwith pellets of the NUCREL and melted for injection molding.

U.S. Pat. No. 5,683,312 discloses a golf ball having a fluid mass at thecenter, a first non-wound mantle layer of a thermoset rubber material,thermoplastic elastomeric material and plastic, a second non-woundmantle layer of a thermoset rubber material or thermoplastic elastomericmaterial, and a cover.

U.S. Pat. No. 5,688,191 discloses a multi-layer golf ball having a corewith one or more layers, at least one cover layer, and one or moremantle layers disposed therebetween, wherein the mantle layer includesdynamically vulcanized thermoplastic elastomer, functionalizedstyrene-butadiene elastomer, thermoplastic polyurethane, metallocenepolymer or blends thereof, and thermoset materials.

It is desirable to use thermoset material-containing hemisphericalshells to form one or more mantle layers about a golf ball center,although this often results in poor centering of the mantle and otherdifficulties because thermoset materials are difficult to work withbefore they have been crosslinked. The polymers typically used in suchshells tend to have a memory that urges the polymer back to its earlieror original shape, which necessitates rapid compression molding tocrosslink the polymer as soon as the shells are formed. Hemisphericalshells are also prone to trapping air in the apex of the mold cavitiesin which they are placed to assemble golf ball cores. Hemisphericalshells also do not tend to readily fit within mold cavities havingoff-center parting lines, which also causes problems due to poorcentering when forming golf ball cores.

There is thus a need for an improved composition and method formanufacturing golf balls that avoids the disadvantages present whenusing thermoset material-containing hemispherical shells to form one ormore mantle layers about a center. A new composition for one or morelayers of a golf ball mantle, and a method for manufacturing a portionof a golf ball core using ellipsoidal shells around a center,advantageously improves the symmetrical formation of the core in golfballs in accordance with the present invention. The proposedcompositions facilitate injection molding of the uncrosslinked shellsand permit automated assembly, which greatly reduces production costs.

SUMMARY OF THE INVENTION

The present invention relates to a method of forming at least a portionof a golf ball core by mixing a resilient polymer component, afree-radical initiator, a crosslinking agent, and a reinforcing polymercomponent to provide an uncrosslinked first mixture having a rigiditymeasured by a flexural modulus of greater than about 3.5 MPa, whereinthe mixing occurs at a temperature greater than the melting temperaturebut sufficiently lower than the crosslinking temperature of thereinforcing polymer component so as to substantially inhibit initiationof crosslinking, forming the first mixture into a plurality of shells ina desired shape, wherein the reinforcing polymer component impartssufficient rigidity to the shells to maintain the desired shape untilthe first mixture is crosslinked, providing a center, assembling atleast two shells concentrically about the center to form a first mantlelayer, wherein the first mantle layer and center together form the ballcore, and applying sufficient heat and pressure to the core as it isconstrained within a rigid cavity for a time sufficient to at leastpartially crosslink the first mixture in the shells, thereby curing atleast a portion of the golf ball core. In a preferred embodiment, thefirst mixture is formed into ellipsoidal shells.

In one embodiment, the method includes selecting the resilient polymercomponent to have a molecular weight average of between about 50,000 to1,000,000. In another embodiment, the reinforcing polymer component isgenerally selected to have a crystalline melting temperature between 35°C. and 120° C. In another embodiment, the first mixture is formed into aplurality of shells by injection molding. These shells are preferablyellipsoidal in shape. In yet another embodiment, the desired ellipsoidalshells are formed by compression molding the first mixture.

In a further embodiment, the ball core has a midpoint and the center ofthe core is disposed within about 0.5 mm from the midpoint. In anotherembodiment, the uncrosslinked first mixture used to form the mantle hasa flexural modulus that is at least about 7 MPa prior to cure. In yetanother embodiment, the loss tangent of the crosslinked mantle materialfirst mixture is adjusted to less than about 0.15 at −60° C. and lessthan about 0.05 at 30° C. at 1 Hz and 1 percent strain. In anotherembodiment, the dynamic modulus, used herein to mean the tensile storagemodulus (E′), of the crosslinked first mixture is greater than about 100MPa at −60° C. and greater than about 50 MPa at 30° C., also at 1 Hz and1 percent strain.

In another embodiment, the melting temperature and the crosslinkingtemperature are selected to differ by about 60° C. to 160° C. In yetanother embodiment, the core is selected to include a center surroundedby elastic windings, a solid center, or a liquid center. In anotherembodiment, at least one additional layer is formed about the centerprior to assembling the shells concentrically about the center, afterassembling the shells concentrically about the center, or after heatingthe core. In a preferred embodiment, at least one additional layer isformed around the core after heating the core to provide a coverdisposed concentrically about the golf ball core.

The invention also relates to elastomeric compositions including aresilient polymer component of at least one polybutadiene having a highmolecular weight average and a 1,4-cis content of greater than about 50weight percent, a free-radical initiator, and an amount of reinforcingpolymer component having a sufficiently low viscosity at a mixingtemperature to facilitate mixing of the reinforcing polymer componentwith the resilient polymer component and having a crystalline meltingpoint sufficiently low to facilitate mixing while avoiding substantialcrosslinking, wherein the uncrosslinked composition has a flexuralmodulus of greater than about 3.5 MPa.

In one embodiment, the composition further includes a crosslinking agentin an amount sufficient to increase crosslinking between the polymercomponents. The invention also relates to an ellipsoidal article formedof the composition.

In another embodiment, the resilient polymer component has a molecularweight from about 50,000 to 1,000,000. In a preferred embodiment, themolecular weight average of the resilient polymer component is fromabout 250,000 to 750,000.

In a further embodiment, the free-radical initiator is an organicperoxide. In another embodiment, the reinforcing polymer componentincludes a block copolymer ether/ester, an acrylic polyol, atranspolyisoprene, a transpolybutadiene, a 1,2-polybutadiene, anethylene-vinyl acetate copolymer, or a cyclooctene. In yet anotherembodiment, the composition also includes a crosslinking agent of ametallic salt selected from the group of an unsaturated fatty acid, amonocarboxylic acid, and mixtures thereof. In another embodiment, thereinforcing polymer component is present in an amount of about 1 to 40weight percent of the resilient and reinforcing polymer components.

The invention also relates to a multi-layer golf ball having a coreincluding a center, a mantle having at least one layer, the layer havinga blend of a reinforcing polymer component and a resilient polymercomponent crosslinked and disposed concentrically adjacent the center,and at least one cover layer disposed concentrically adjacent the mantleand outwardly thereof, wherein the uncrosslinked mantle layer issufficiently rigid to inhibit the resilient polymer component fromsubstantially altering shape prior to crosslinking.

In another embodiment, the resilient polymer component and the core eachinclude polybutadiene, natural rubber, polyisoprene, styrene-butadiene,or styrene-propylene-diene rubber, or mixtures thereof. In a preferredembodiment, the resilient polymer component is 1,4-cis-polybutadienehaving a 1,4-cis content of greater than about 50 weight percent. In apreferred embodiment, the 1,4-cis content is greater than about 90weight percent.

In still another embodiment, the amount of resilient polymer componentis between about 60 to 99 weight percent of the polymer components. In apreferred embodiment, the amount of resilient polymer component presentis from about 75 to 90 weight percent of the polymer components. Inanother embodiment, the golf ball core further includes at least one ofa filler, a free-radical initiator, or a crosslinking agent. In onepreferred embodiment, filler is present and includes masterbatch red,zinc oxide, tin oxide, barium sulfate, zinc sulfate, calcium carbonate,barium carbonate, clay, tungsten, tungsten carbide, a silica, ortrimethyl-tripropane, or mixtures thereof, present in an amount fromabout 0.5 to 50 weight percent of the mantle. In another preferredembodiment, the free-radical initiator is an organic peroxide. Inanother preferred embodiment, the crosslinking agent includes a metallicsalt selected from the group of an unsaturated fatty acid, amonocarboxylic acid, and mixtures thereof. In another embodiment, theuncrosslinked mantle layer has a flexural modulus of greater than about3.5 MPa.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the invention can be ascertained fromthe following detailed description which is provided in connection withthe attached drawings, wherein:

FIG. 1 illustrates two semi-ellipsoidal shells being assembled about acenter according to the invention;

FIG. 2 illustrates a view of two shells having exaggerated-scalesemi-ellipsoidal shapes being assembled about a center, and locatedwithin a mold cavity, according to the invention; and

FIG. 3 illustrates a multilayer golf ball having a center, a mantle withseveral layers, and a cover according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

Resilient polymer components, such as polybutadiene, typically have a“memory” that forces reshaped components to attempt to return to theiroriginal or previous shape. It has now been discovered that the additionof a reinforcing polymer component to the resilient polymer componentimparts reinforcement that inhibits or prevents the resilient polymerfrom relaxing to an earlier or original position that may result information of an off-center ball during further processing. Thereinforcing polymer component imparts geometrical stability to theuncrosslinked material used to form the mantle, at least in part byinhibiting shifting of the mantle during assembly about the center.

The center of the ball is typically and preferably spherical, may besolid or liquid-filled, and is generally about 0.5 inches to 1.5 inches,preferably about 0.8 inches to 1.3 inches, and more preferably about 1to 1.2 inches in diameter. It is envisioned that an elastic strip may bewound around the center and before the mantle is added, although it ispreferred that the mantle be placed around the center withoutintervening layers. The mantle should have a thickness of about 0.1 to0.6 inches, preferably about 0.15 to 0.35 inches, more preferably about0.2 to 0.3 inches. The entire core, including the center and mantle,should have a diameter of about 1.25 to 1.65 inches, preferably 1.38 to1.6 inches, where twice the mantle thickness is included in the corediameter since the mantle encloses the center. The diameter of themantle corresponding to a particular center, and of the cover formedaround the mantle and center, may be adjusted according to the diameterof the center to provide a golf ball formed according to the inventionwith the overall minimum diameter required by the USGA. The mantleshould be thick enough to form the core when molded over the center. Theminimum mantle thickness is readily determined by one of ordinary skillin the art, and depends upon the specific materials used to form themantle. One example of a preferred ball center size according to theinvention is a center having a diameter of 1.08 inches and a mantlehaving a thickness of 0.25 inches to provide a core having a 1.58 inchdiameter.

The present invention includes a novel composition and method of makinga ball and a portion of a ball, and the ball and ball portions therebyproduced, to advantageously improve the centering of the mantle relativeto the center of a ball. Improved centering of the mantle about thecenter results in a more symmetrical ball core. Although the methods andcompositions of the invention are suitable for making other types ofballs, they are best used for golf balls. The composition of theinvention is advantageously used in forming a plurality of shells thatare assembled about a center and that form at least one layer of themantle. The shells and resultant mantle include a reinforcing polymercomponent, a resilient polymer component, a free-radical initiator, andoptionally one or more of a crosslinking agent and fillers.

The composition and method of the invention offer significant advantagesover the prior art. For example, the invention permits air in the apexof the mold cavities to be more easily removed, permits the shells to beformed by injection molding and to more readily fit within mold cavitieshaving off-center parting lines, and provides improved centering of themantle about the center when forming golf ball cores.

The shells, and resultant mantle, for use in a ball core include aresilient polymer component, which is used as the majority of polymer inthe composition and method. Resilient polymers suitable for use in theball core include polybutadiene, polyisoprene, styrene-butadiene,styrene-propylene-diene rubber (EPDM), mixtures thereof, and the like.The resilient polymer component is preferably polyisoprene orpolybutadiene (“PBD”), more preferably polybutadiene, and mostpreferably a 1,4-cis-polybutadiene. One example of a1,4-cis-polybutadiene is CARIFLEX BR 1220, commercially available fromH. MUEHLSTEIN & CO., INC. of Norwalk, Conn. The polybutadiene or otherresilient polymer component may be produced with any suitable catalystthat results in a predominantly 1,4-cis content, and preferably with acatalyst that provides a high 1,4-cis content and a high molecularweight average. The resilient polymer component has a high molecularweight average, defined as being at least about 50,000 to 1,000,000,preferably from about 250,000 to 750,000, and more preferably from about200,000 to 325,000. CARIFLEX BR 1220 has a molecular weight average ofabout 220,000. The 1,4-cis component of polybutadiene is generally thepredominant portion of the resilient polymer component whenpolybutadiene is present. “Predominant” or “predominantly” is usedherein to mean greater than 50 weight percent. The 1,4-cis component ispreferably greater than about 90 weight percent, and more preferablygreater than about 95 weight percent, of the polybutadiene component.The resilient polymer component is typically present in an amount of atleast about 60 weight percent, preferably about 65 to 99 weight percent,and more preferably about 75 to 90 weight percent of the polymer blend.The term “polymer blend” is used herein to mean the blend of theresilient polymer component and the reinforcing polymer component. Theresilient polymer component imparts resilience to the core or mantle inthe cured, or crosslinked, state.

The mantle also includes a reinforcing polymer component, which containsat least one polymer having a glass transition temperature sufficientlylow to permit combination and mixing of the reinforcing polymercomponent with the resilient polymer component without initiatingcrosslinking of the crosslinking agent that is also typically present inthe mixture, as described below. The reinforcing polymer componentshould have a sufficiently low viscosity at the mixing temperature whenmixed with the resilient polymer component to permit proper mixing ofthe two polymer components. The reinforcing polymer component alsotypically has a glass transition temperature (and if crystalline, acrystalline melting point) sufficiently low to permit mixing with theresilient polymer component while avoiding substantial crosslinking orthermal degradation of the resilient component at the mixingtemperature. The crystalline melting temperature is typically betweenabout 35° C. to 120° C. Examples of polymers suitable for use as thereinforcing polymer component include: transpolyisoprene, blockcopolymer ether/ester, acrylic polyol, a polyethylene, a polyethylenecopolymer, 1,2-polybutadiene (syndiotactic), ethylene-vinyl acetatecopolymer, cyclooctene, trans-polybutadiene, and mixtures thereof.Particularly suitable reinforcing polymers include: HYTREL 3078, a blockcopolymer ether/ester commercially available from DuPont of Wilmington,Del.; a transpolybutadiene, such as FUREN 88 obtained from AsahiChemicals of Yako, Kawasakiku, Kawasakishi, Japan; KURRARAY TP251, atranspolyisoprene commercially available from KURRARAY CO. of New York,N.Y. as KURRARAY AMERICA CO.; LEVAPREN 700HV, an ethylene-vinyl acetatecopolymer commercially available from Bayer-Rubber Division, Akron,Ohio; and VESTENAMER 8012, a cyclooctene commercially available fromHuls America Inc. of Tallmadge, Ohio. Some suitable reinforcing polymercomponents are listed below with their crystalline melting points and/orT_(g).

Crystalline Melt Temperature Polymer Type Tradename (° C.) T_(g) (° C.)Transpolyisoprene KURRARAY TP251 60 −59 Transpolybutadiene FUREN 88 84−88 Polyethylene Dow LPDE 98 −25 Polyoctene VESTENAMER 8012 54 −65

The reinforcing polymer component must be present in an amountsufficient to impart rigidity to the shells during processing, yet notundesirably reduce resilience of the crosslinked polymer blend andthereby have an undesirable effect on the final product. Also, thereinforcing polymer component, i.e., the additive polymer component,must have a viscosity sufficiently low to permit mixing of thereinforcing polymer component and the resilient polymer component. Forexample, transpolyisoprene has a viscosity of less than 1,000,000 poiseat a mixing temperature of around 82° C. The viscosity of materialssuitable for use in the invention may be readily determined by one ofordinary skill in the art. The viscosity should generally be below about1,000,000 poise to readily permit mixing. When transpolyisoprene is usedas the reinforcing polymer component, it is typically present in anamount of about 10 to 40 weight percent, preferably about 15 to 30weight percent, of the polymer blend. The weight of the reinforcingpolymer relative to the total composition generally ranges from about 5to 25 weight percent, preferably about 10 to 15 weight percent. Theuncrosslinked mantle should have a flexural modulus, as measured underASTM D790M-93, Method II, of greater than about 3.5 MPa, and preferablygreater than about 7 MPa. The reinforcing polymer components imparts adegree of rigidity to the shells sufficient to maintain the desiredshape until the first mixture is crosslinked.

Suitable crosslinking agents include one or more metallic salts ofunsaturated fatty acids or monocarboxylic acids, such as zinc, calcium,or magnesium acrylate salts, and the like. Preferred acrylates includezinc acrylate, zinc diacrylate, and zinc methacrylate. The crosslinkingagent must be present in an amount sufficient to crosslink the variouschains of polymers in the polymer blend to themselves and to each other.The desired elastic modulus for the mantle may be obtained by adjustingthe amount of crosslinking by selecting a particular type or amount ofcrosslinking agent. This may be achieved, for example, by altering thetype and amount of crosslinking agent, which method is well known tothose of ordinary skill in the art. The crosslinking agent is typicallyadded in an amount from about 1 to 50 parts per hundred of the polymerblend, preferably about 20 to 45 parts per hundred, and more preferablyabout 30 to 40 parts per hundred, of the polymer blend.

Although not required, a free-radical initiator is preferably includedin the composition and method. The free-radical initiator may be anycompound or combination of compounds present in an amount sufficient toinitiate a crosslinking reaction between a crosslinking agent and thereinforcing and resilient polymer components of the polymer blend. Thefree-radical initiator is preferably a peroxide. Suitable free-radicalinitiators include di(2-t-butyl-peroxyisopropyl)benzene peroxide,1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, dicumyl peroxide,di-t-butyl peroxide, 2,5-di-(t-butylperoxy)-2,5-dimethyl hexane,n-butyl4,4-bis(t-butylperoxy)valerate on calcium silicate, lauroylperoxide, benzoyl peroxide, t-butyl hydroperoxide, and the like. Thefree-radical initiator is preferably present in an amount of up to 2parts per hundred, more preferably about 0.2 to 1 parts per hundred ofthe polymer blend.

The resilient polymer component, reinforcing polymer component,free-radical initiator, and any other materials used in forming the golfball core in accordance with invention may be combined by any type ofmixing known to one of ordinary skill in the art. A suitable system, forexample, would include transpolyisoprene, which melts at around 60° C.,as the reinforcing component and a dicumyl peroxide, which substantiallyinitiates reaction at around 170° C., as the free radical initiator.Suitable types of mixing include single pass and multi-pass mixing, andthe like. The optional crosslinking agent, and any other optionaladditives used to modify the characteristics of the golf ball center,may similarly be combined by any type of mixing. A single-pass mixingprocess where ingredients are added sequentially is preferred, as thistype of mixing tends to increase efficiency and reduce costs for theprocess. Suitable mixing equipment is well known to those of ordinaryskill in the art, and such equipment may include a Banbury mixer or atwin screw extruder. Conventional mixing speeds for combining polymersare typically used, although the speed must be high enough to impartsubstantially uniform dispersion of the resilient and reinforcingpolymer components. On the other hand, the speed should not be too high,as high mixing speeds tend to break down the polymers being mixed andparticularly may undesirably decrease the molecular weight of theresilient polymer component. The speed should thus be low enough toavoid high shear, which may result in loss of desirably high molecularweight portions of the resilient polymer component. Also, too high amixing speed may undesirably result in creation of enough heat toinitiate the crosslinking before the preforms are shaped and assembledaround a core. The mixing temperature depends upon the type of resilientand reinforcing polymer components, and more importantly, on the type offree-radical initiator. The mixing temperature must be higher than themelting temperature of the reinforcing polymer component, but not sohigh as to initiate substantial crosslinking. For example, when usingdi(2-t-butyl-peroxyisopropyl)benzene peroxide as the free-radicalinitiator, a mixing temperature of about 80° C. to 125° C., preferablyabout 88° C. to 110° C., and more preferably about 90° C. to 100° C. issuitable to safely mix the ingredients. The mixing speed and temperatureare readily determinable by one of ordinary skill in the art withoutundue experimentation.

Fillers are typically also added to the composition used in the shellsof the mantle, the center, or both ball portions, to increase thedensity of the core to conform to uniform golf ball standards. Fillersmay also be used to modify the weight of the core for specialty ballsused by players, e.g., a lower weight core is preferred for a playerhaving a low swing speed. Fillers typically include processing aids orcompounds to affect rheological and mixing properties, the specificgravity, the modulus, the tear strength, reinforcement, and the like.The fillers are generally inorganic, and suitable fillers includenumerous metals and metal oxides, such as zinc oxide and tin oxide, andbarium sulfate, zinc sulfate, calcium carbonate, barium carbonate, clay,tungsten, tungsten carbide, an array of silicas, trimethyl-tripropane,and the like. The fillers, when used, may be present in an amount ofabout 0.5 to 50 weight percent of the composition.

Any conventional material or method may be used in preparing the golfball cover disposed over the core. For example, as is well known in theart, ionomers, balata, and urethanes are suitable golf ball covermaterials. A variety of less conventional materials may also be used forthe cover, e.g., thermoplastics such as ethylene- or propylene-basedhomopolymers and copolymers. These homopolymers and copolymers may alsoinclude functional monomers such as acrylic and methacrylic acid, fullyor partially neutralized ionomers and their blends, methyl acrylate,methyl methacrylate homopolymers and copolymers, imidized aminogroup-containing polymers, polycarbonate, reinforced polycarbonate,reinforced polyamides, polyphenylene oxide, high impact polystyrene,polyether ketone, polysulfone, poly(phenylene sulfide),acrylonitrile-butadiene, acrylic-styrene-terephthalate, poly(ethyleneterephthalate), poly(butylene terephthalate), poly(ethylene-vinylalcohol), poly(tetrafluoroethylene), and the like. Any of these polymersor copolymers may be further reinforced by blending with a wide range offillers, including glass fibers or spheres, or wood pulp. The selectionof a suitable cover, and application thereof over the mantle describedherein, will be readily determinable by those of ordinary skill in theart when considering the disclosure herein.

The golf balls of the present invention, or portions thereof, areprepared as follows. A solid spherical center including one or more ofthe resilient polymer components described herein is prepared by atleast one of conventional compression, injection molding, or windingtechniques. A liquid-filled center may alternatively be formed insteadof a solid center. Any additionally desired center layers may then beadded to the center by conventional compression or injection moldingtechniques, preferably in a concentric fashion to maintain asubstantially spherical center.

The mantle preforms may be prepared as ellipsoidal or hemisphericalhalf-shells using conventional compression or injection moldingtechniques. The preferred method is to prepare two ellipsoidalhalf-shells that fit around the core and merge to form the mantle, orone or more layers thereof. The ellipsoidal half-shells, also known aspreps or preforms, preferably have a minor axis of 0.9 to 0.98 times anda major axis of 1 to 1.5 times, preferably 1.02 to 1.1 times the moldcavity diameter when two half-shells are combined to form a mantle. Themajor and minor axes are measurements of the combination of two adjacenthalf-shells assembled about a center. The major and minor axes havedifferent sizes due to the ellipsoidal shape of pairs of preforms, andif a pair of preforms were spherical the major and minor axes would bethe same size and would each be equal to a diameter of the sphere formedby the two preforms. The ellipsoidal preforms thus have thicker crownsat their top and bottom and a thinner equator, i.e., ellipsoidal inshape, than a conventional spherical mantle which would have a constantdiameter at any orientation.

The preforms are prepared by mixing the resilient polymer component, thereinforcing polymer component, and any other ingredients together asdiscussed above. The resulting geometrical stability provides additionaltime for processing between preform formation and curing via compressionmolding. This additional time may be used to improve manufacturability,optimize production scheduling, and the like, such as by preparation andstockpiling of rigid shells to facilitate molding machine shut down formaintenance or tool changes. With enough shells stockpiled, further golfball manufacture could be carried out even while the preform injectionmachine is being retooled. The mixture of polymer components,free-radical initiator, optionally a crosslinking agent, and any fillersmay be extruded or pelletized for introduction into a molding machinefor preparation of the mantle.

The ellipsoidal half-shells are preferably injection molded from themixture based on cost and speed considerations, although compressionmolding is also suitable. The mold is preferably maintained at atemperature below the crystalline melting temperature of the reinforcedpolymer component to inhibit the formed shells from altering shape dueto the memory of the resilient polymer component.

After their formation, the ellipsoidal half-shells are assembled aboutthe core. In accordance with the invention, the shells may be producedrapidly with injection molding. The rapid production of shells permitsuse of automated procedures for assembly about the center. Duringassembly about the center, the ellipsoidal half-shells self-orientthemselves vertically when placed in hemispherical mold cups, whichreduces preparation time, cost, and defects. The ellipsoidal shellsinhibit formation of air cavities at the apex due to their having morematerial at the crown of the shell, thereby facilitating the expulsionof any trapped air out of the mold at the equator of the core where thetwo mold halves are typically combined for the molding of the mantleabout the center. The assembly of the core, i.e., typically twohalf-shell preforms and a center, may be compression molded. When themold halves are combined, they form a rigid, spherical cavity. Once themold is closed, the excess material from the shell crowns is forced outof the mold cavity at the equator where the mold halves combine. Thecompression molding of the assembled preforms and center tends to takeabout 5 to 40 minutes, although times may vary depending upon thematerials used. For example, a typical compression molding cycle maytake 12 minutes at around 174° C. The shells are forced together by themold and substantially cured during molding. Optionally, if additionalmantle layers are desired, e.g., having different characteristics toimprove or modify the overall ball qualities, they may be provided overthe first mantle layer. Additional mantle layers are preferably addedafter the previous mantle layer is cured, although they may be addedbefore cure of the previous layer if the pre-cured mantle layer is rigidenough so that substantially no mixing of the layers occurs.

Balls prepared according to the invention with a reinforcing polymercomponent in the mantle tend to exhibit substantially the sameresilience, or coefficient of restitution, as balls with conventionalmantles. Another measure of this resilience is the “loss tangent,” ortan δ, which is obtained by measuring the dynamic visco-elasticity of anobject. Thus, a lower loss tangent indicates a higher resiliency,thereby indicating a higher rebound capacity. Loss tangent and a varietyof other dynamic properties may be measured according to ASTM D4065-90,and terminology relating to such dynamic properties is typicallydescribed according to ASTM D4092-90. Low loss tangent indicates thatmost of the energy imparted to a golf ball from the club is converted todynamic energy, i.e., launch velocity and resulting longer distance. Thedesired loss tangent in the crosslinked mantle material should be lessthan about 0.15 at −60° C. and less than about 0.05 at 30° C. whenmeasured at a frequency of 1 Hz and a one percent strain. The rigidityor compressive stiffness of a golf ball may be measured, for example, bythe dynamic modulus. A higher dynamic modulus indicates a highercompressive stiffness. To produce golf balls having a desirablecompressive stiffness, and therefore a suitable “feel” to the player,the dynamic modulus of the crosslinked mantle material should be greaterthan about 100 MPa at −60° C. and greater than about 50 MPa at 30° C.measured at 1 Hz and one percent strain.

FIG. 1 illustrates semi-ellipsoidal shells 2 being assembled about agolf ball center 5 according to the invention. The shells are joined atthe equator 7.

FIG. 2 illustrates an exaggerated-scale view of two shells 2 havingsemi-ellipsoidal shapes according to the invention being assembled abouta center 5 in a compression molding device 10. The molding devicepreferably contains a hemispherical, concave chamber 15 to form half ofthe core. The equator 7 of the two shells is depicted, showing where thetwo semi-ellipsoidal shells 2 contact each other about the center 5. Theapex 12 of the shells 2 contains additional material relative to theside portions by the mutual equator 7 of the shells 2. When the mold 10is closed and heated, the two hemispherical, concave chambers 15together form a spherical chamber to provide a final substantiallyspherical shape to the core. Excess material from the semi-ellipsoidalshells 2 flows out of the chamber at the interface between the moldhalves, i.e., at the equator 7, resulting in a final center that iscrosslinked and substantially spherical.

The resulting ball, after a suitable cover is applied by conventionaltechniques, exhibits improved characteristics such as the low spin andhigh coefficient of restitution desired by the vast majority of golfplayers. The semi-rigid ellipsoidal shells, as a result of combining thereinforcing polymer component and resilient polymer component, have asubstantially improved concentricity of the mantle in relation to thecore, and require less labor to produce. For example, the center of aball core prepared according to the invention is typically no more thanabout 0.5 mm from the center of the cured golf ball. One of ordinaryskill in the art of golf ball manufacture, as well as the typicalplayer, will readily recognize that more accurate centering of the ballresults in more consistent results and an improved game.

Similarly, FIG. 3 illustrates a multi-layer solid golf ball with a cover20 and a core with a mantle assembled about a center 5 according to theinvention. In this embodiment, the mantle includes two mantle layers 22and 25 according to the invention.

EXAMPLES

The following examples are provided only for the purpose of illustratingthe invention and are not to be construed as limiting the invention inany manner.

Examples 1-9

Exemplary Mantle Compositions

Sample mantle compounds were prepared and mixed according to thetechniques described herein. The following mantle formulations 1-9 wereprepared:

Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Ex. 8 Ex. 9 Component PHR/wt %PHR/wt % PHR/wt % PHR/wt % PHR/wt % PHR/wt % PHR/wt % PHR/wt % PHR/wt %Zinc diacrylate 38/23.8   34/21.7 30/19.4 26/17.1 22/14.7   24/15.7  20/13.4   16/10.9  12/8.3 Zinc oxide 21/13.1 22/14 24/15.5 25/16.527/18    28/18.3   29/19.4   30/20.4   32/22.1 Transpolyisoprene 20/12.5  20/12.8 20/12.9 20/13.2 20/13.4 0/0 0/0 0/0 0/0 (Reinforcing Comp.)High MW 1,4-cis- 80/50.1 80/51 80/51.7 80/52.7 80/53.4  100/65.4 100/66.8  100/68.1  100/69.1 PBD 1,1-bis(t- 0.42/0.26  0.42/0.270.42/0.27  0.4/0.28  0.42/0.28  0.42/0.27 0.42/0.28 0.42/0.29 0.42/0.29butylperoxy)-3,3,5- trimehtylcyclohexane di(2-t-butyl- 0.15/0.09 0.15/0.1  0.15/0.1  0.15/0.1  0.15/0.1  0.15/0.1  0.15/0.1  0.15/0.1 0.15/0.1  peroxyisopropyl) benzene Color masterbatch 0.25/0.16  0.25/0.16 0.25/0.16  0.25/0.16  0.25/0.17  0.25/0.16 0.25/0.17 0.25/0.170.25/0.17 PHR is parts per hundred. Color masterbatch is a filler thatsimply provides a colored composition. Examples 6-9 are exemplary centercompositions used with mantles of the invention.

The formulations described in Examples 1-5 above are but a few examplesof compositions usable in the method of the present invention to form amantle layer in a golf ball that exhibits improved centering. Examples6-9 are sample formulations for conventional golf ball centers.

Examples 10-12

Flexural Modulus of Mantles Prepared According to the Invention

A flex bar specimen having the dimensions {fraction (3/16)}″×½″×4″ wasproduced by compression molding uncrosslinked mantle material. Theflexural modulus of uncrosslinked mantles prepared according to theinvention was measured using ASTM Method D790M-93, Method II, with aloading rate of 0.5 in/min.

Reinforcing Component Example # Amount* Flexural Modulus (MPa) 10 13.1%7.6 11 19.8% 13 12 26.6% 21.5 *The Reinforcing Polymer Component Amountis a percentage based on the total weight of the resilient andreinforcing polymer components.

The formulations of Examples 6-9, which did not contain a reinforcingpolymer component, had an insufficient rigidity to form flexure bars,thereby preventing determination of the flexural modulus.

Examples 13-15

Improved Centering According to the Invention

Three types of golf balls were tested after cure to determine the degreeof accuracy in concentricity. Measured values included the averageshift, maximum shift, and minimum shift, of the mantle from the midpointof the ball. The standard deviation (“STD”) was also calculated.

Avg. Shift Max Shift Min. Shift Example # (mm) STD (mm) (mm) (mm) 130.035 0.023 0.125 0.009 (Conventional) 14 0.014 0.011 0.052 0.001 150.015 0.02 0.065 0.001

Example 13 was a competitor's core prepared with conventional materials,which resulted in a typically off-center ball. Examples 14-15 wereprepared using the materials and methods of the present invention, andclearly resulted in a highly improved concentricity.

Examples 16-23

Comparative Spin Rates of Golf Balls

Several conventional golf balls were tested along with several ballsprepared according to the invention using a standard driver to determinetheir spin rates, launch speeds, and compression. The test ballsprepared according to the invention all have mantles with 20 PHR Balata,centers having a 1.15 inch diameter, cores having a 1.58 inch diameter,and conventional ionomer covers having a blend of the following DuPontSURLYN® polymers: 30 weight percent DuPont 8320, 40 weight percentDuPont 7940, 10 weight percent DuPont 8660, and 20 weight percent DuPont8940.

Spin Speed Compression Ball Type (rev/min.) (ft/s) (Atti gauge)Conventional Single 3015 159 95 Layer Ball Conventional Multi- 2902 15576 layer Ball Mantle of Ex. 5 w/ 3204 155 54 Center of Ex. 7 Mantle ofEx. 2 w/ 3051 159 88 Center of Ex. 7 Mantle of Ex. 1 w/ 2970 158 84Center of Ex. 8 Mantle of Ex. 4 w/ 3130 155 62 Center of Ex. 7 Mantle ofEx. 2 w/ 2972 158 80 Center of Ex. 8 Mantle of Ex. 1 w/ 3049 159 91Center of Ex. 7

These examples advantageously illustrate that the balls preparedaccording to the invention have spin and initial speed comparable to, orbetter than, spin rates and speeds of conventional balls, while at thesame time permitting a more cost effective production and easierpreparation. The Atti Compression Gauge is commercially available fromAtti Engineering Corp. of Union City, N.J.

Examples 24-29

Comparative Spin Rates of Golf Balls

Several additional balls were prepared according to Examples 16-23, andsimilarly tested using a standard driver to determine their spin rates,launch speeds, and compression.

Spin Compression Ball Type (rev/min.) Speed (ft/s) (Atti gauge) Mantleof Ex. 3 w/ 2640 154 67 Center of Ex. 8 Mantle of Ex. 4 w/ 3366 157 69Center of Ex. 7 Mantle of Ex. 3 w/ 2933 157 73 Center of Ex. 7 Mantle ofEx. 2 w/ 2824 154 72 Center of Ex. 9 Mantle of Ex. 5 w/ 3386 157 63Center of Ex. 6 Mantle of Ex. 1 w/ 2705 154 74 Center of Ex. 9

These examples further illustrate that the balls prepared according tothe invention have spin and initial speed comparable to, or better than,spin rates and speeds of conventional balls, while at the same timepermitting a more cost effective production and easier preparation.

It is to be recognized and understood that the invention is not to belimited to the exact configuration as illustrated and described herein.For example, it should be apparent that a variety of suitable materialswould be suitable for use in the composition or method of making thegolf balls according to the Detailed Description of the Invention.Accordingly, all expedient modifications readily attainable by one ofordinary skill in the art from the disclosure set forth herein aredeemed to be within the spirit and scope of the present claims.

What is claimed is:
 1. A golf ball comprising: a core formed from acomposition comprising: a resilient polymer component of at least onepolybutadiene having a high molecular weight average and a 1,4-ciscontent of greater than about 50 weight percent; a free-radicalinitiator; and an amount of reinforcing polymer component having asufficiently low viscosity at a mixing temperature to facilitate mixingof the reinforcing polymer component with the resilient polymercomponent and having a crystalline melting point sufficiently low tofacilitate the mixing while avoiding substantial crosslinking, whereinthe uncrosslinked composition has a flexural modulus of greater thanabout 3.5 Mpa; and a cover formed from a composition comprising at leastone ionomer or at least one urethane.
 2. The golf ball of claim 1,wherein the core composition further comprises a crosslinking agent inan amount sufficient to increase crosslinking between the polymercomponents.
 3. The golf ball of claim 1, wherein the resilient polymercomponent has a molecular weight from about 50,000 to 1,000,000.
 4. Thegolf ball of claim 3, wherein the molecular weight average of theresilient polymer component is from about 250,000 to 750,000.
 5. Thegolf ball of claim 1, wherein the free-radical initiator is an organicperoxide.
 6. The golf ball of claim 1, wherein the reinforcing polymercomponent comprises a block copolymer ether/ester, an acrylic polyol, atranspolyisoprene, a transpolybutadiene, a 1,2-polybutadiene, anethylene-vinyl acetate copolymer, a polyethylene or copolymer thereof,or a cyclooctene.
 7. The golf ball of claim 2, wherein the crosslinkingagent comprises a metallic salt selected from the group consisting of anunsaturated fatty acid, a monocarboxylic acid, and mixtures thereof. 8.The golf ball of claim 1, wherein the reinforcing polymer component ispresent in an amount of about 1 to 40 weight percent of the resilientand reinforcing polymer components.
 9. The golf ball of claim 1, whereinthe ionomer is fully or partially neutralized.
 10. A multi-layer golfball comprising: a core having a diameter of about 1.25 inches to about1.65 inches comprising: a center; and a mantle comprising at least onelayer, the layer comprising a blend of a reinforcing polymer componentand an uncrosslinked resilient polymer component, wherein the mantle isdisposed concentrically adjacent the center; and at least one coverlayer disposed concentrically adjacent the mantle and outwardly thereof,wherein the uncrosslinked mantle layer is sufficiently rigid to inhibitthe resilient polymer component from substantially altering shape priorto crosslinking.
 11. The ball of claim 10, wherein the resilient polymercomponent of the core comprises polybutadiene, natural rubber,polyisoprene, styrene-butadiene, or styrene-propylene-diene rubber. 12.The ball of claim 11, wherein the resilient polymer component is1,4-cis-polybutadiene having a 1,4-cis content of greater than about 50weight percent.
 13. The ball of claim 12, wherein the resilient polymercomponent comprises a high molecular weight average is1,4-cis-polybutadiene.
 14. The ball of claim 13, wherein the resilientpolymer component comprises 1,4-cis-polybutadiene having a molecularweight average of about 50,000 to 1,000,000.
 15. The ball of claim 10,wherein the amount of resilient polymer component is between about 60 to99 weight percent of the total weight of polymer components.
 16. Theball of claim 10, further comprising at least one of a filler, afree-radical initiator, or a crosslinking agent.
 17. The ball of claim16, wherein the filler comprises masterbatch red, zinc oxide, tin oxide,barium sulfate, zinc sulfate, calcium carbonate, barium carbonate, clay,tungsten, tungsten carbide, a silica, ground rubber, ortrimethyl-tripropane present in an amount from about 0.5 to 50 weightpercent of the mantle.
 18. The ball of claim 16, wherein thefree-radical initiator is an organic peroxide.
 19. The ball of claim 16,wherein the crosslinking agent comprises a metallic salt selected fromthe group consisting of an unsaturated fatty acid, a monocarboxylicacid, and mixtures thereof.
 20. The ball of claim 10, wherein theuncrosslinked mantle layer has a flexural modulus of greater than about2.5 MPa.
 21. The ball of claim 10, wherein the at least one cover layercomprises at least one of an ionomer, balata or urethane.
 22. The ballof claim 21, wherein the ionomer is fully neutralized.
 23. The ball ofclaim 10, further comprising a layer disposed between the mantle layerand the at least one cover layer.
 24. The ball of claim 10, wherein thereinforcing polymer component has a viscosity of less than about1,000,000 poise.